Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., downhole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device downhole. To obtain such measurements, magnetometers are sometimes applied to provide telemetry, ranging, and bit location functions.
Magnetometers with very low noise floors have recently become available. For example, some references for magnetometers quote noise floors on the order of 10 pT RMS/√{square root over (Hz)}. In order to reach such low noise floors, these magnetometers may be built with a soft magnetic core with high relative permeability. However, magnetometers built with these soft magnetic cores may not operate reliably at high temperatures.